UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item ODONATA SPECIES COMPOSITION IN AGROECOSYSTEMS: PRELIMINARY SURVEYS WITH AN EMPHASIS ON POTENTIAL FOR BIOLOGICAL CONTROL ON FARMS(2024) Hartman, Margaret Elizabeth; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Adult dragonflies and damselflies are efficient aerial predators that provide ecosystem service as consumers of pest arthropods. However, their role as predators of agricultural pests in agroecosystems has been understudied. The prey of odonates has been historically difficult to quantify but new molecular methods can make diet analysis easier. I conducted visual encounter surveys across four farms in 2020 and 2021. I found odonates were present on all farms surveyed but there were significant differences in abundance and richness. Fecal pellets were collected from 94 odonates in 2021 for prey DNA analysis using next generation sequencing. Nine odonate samples produced exceptional libraries, resulting in a large quantity of identifiable prey sequences. This preliminary study can help future researchers develop best practices for maintaining healthy farm water bodies and optimizing fecal DNA analysis methodology to better understand odonates’ potential for agricultural pest suppression.Item BIODIVERSITY AND CONSERVATION BIOLOGICAL CONTROL: DO BUFFER STRIPS WITH WILDFLOWERS ENHANCE NATURAL ENEMIES IN NEIGHBORING CROP HABITATS?(2010) Moore, Laura; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Grass buffer strips are commonly deployed along crop borders in North American agricultural landscapes. Such borders filter nutrient and pesticide runoff to neighboring habitats and foster biodiversity. The addition of wildflowers in these strips to provide nectar and pollen resources can positively impact natural enemies of crop pests, particularly hymenopteran parasitoids. I investigated the presence/absence of wildflowers on natural enemy abundance in buffer strips and in neighboring soybean fields in 2005 and 2006. I predicted that wildflowers would attract and act as a source of natural enemies which would then disperse into neighboring crop fields. In both years, sticky cards were used to measure the abundance of aerial arthropods in pure stands of wildflowers and in neighboring soybean plots. Pitfall traps were also used in 2006 to measure abundance of epigeal taxa. In the 2005 experiment, sticky card captures of hymenopteran and dipteran parasitoids were 72.7% higher in buffers containing partridge pea compared to the other buffer types. Similarly, communities of all beneficial arthropods captured by sticky card and pitfall traps in 2006 were significantly 79.8% to 72.3 % higher, respectively, in the partridge pea buffers compared to communities in the soybean crop. However, buffer effects on populations of parasitoids and predators in the neighboring crop were mixed in both experiments depending on the particular functional group and specific family of arthropods. Results suggest that partridge pea was a source for canopy-dwelling dipteran parasitoids and saprovores, but acted as a sink for canopy-dwelling mymarids, canopy-dwelling predators and ground-dwelling ants, and had a neutral effect on all others. However, these effects did not extend far into the soybean crop and were generally not discernible beyond 6m. This study provides evidence that a pure stand of an attractive source of floral resources in a bordering non-crop area may not be desirable for enhancing conservation biological control. The species of flower and desired natural enemy should be taken into consideration before determining the mix of plant species to include in a buffer strip.Item ROLE OF PEACH [PRUNUS PERSICA (L.) BATCSH] EXTRAFLORAL NECTARIES IN MEDIATING NATURAL ENEMY-HERBIVORE INTERACTIONS(2004-11-30) Mathews, Clarissa Ruth; Bottrell, Dale G.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Extrafloral nectaries (EFNs) are reported to benefit some plants when ants (Hymenoptera: Formicidae) use their secretions and fend off herbivores. The significance of peach [Prunus persica (L.) Batcsh] EFNs in mediating natural enemy-pest dynamics was studied for the 'Lovell' cultivar with EFNs present and absent. The first phase of the research tested the hypothesis that peach EFNs contribute indirectly to plant defense from herbivores. Trees with EFNs experienced a 6-fold increase in predators (predominantly ants), fewer herbivores, and less folivory compared to trees without EFNs. Ant exclusion techniques further revealed that trees with EFNs benefited from reduced folivory in the spring and increased vigor (trunk circumference, leaf surface area, and terminal carbon composition) only when ants were permitted in their canopies. It was concluded that the EFNs do have a defensive role with regard to foliage feeders. The next research phase explored the impact of EFNs on biological control of a key economic pest, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), in peach orchards. Experiments revealed that trees with EFNs had higher parasitoid densities in the spring and increased parasitism of larval G. molesta later in the season. Ant exclusion from mature peach trees with EFNs increased G. molesta fruit injury by > 4-fold, indicating that EFNs have a protective role for the fruit as well. The potential for competitive interactions between ants and other natural enemies associated with EFNs was explored in the final research phase. Studies revealed that several natural enemy groups contribute to reductions in G. molesta eggs, larvae, and pupae in peach orchards. Although ants antagonized the G. molesta egg parasitoid Trichogramma minutum (Riley) on trees with EFNs, the ants were crucial in reducing G. molesta in both the larval and pupal stages. The implications of EFN-natural enemy-pest interactions to orchard-level biological control will likely depend on local herbivore population dynamics. However, the EFNs clearly benefit P. persica indirectly, through enhancement of ants and other natural enemies. Thus, EFNs are an important host-plant characteristic that should be retained in future peach cultivars in order to maximize conservation biological control.